A step forward parameter for the effects of transcatheter aortic valve implantation: transmural dispersion of repolarization.

We have recently reported a potential beneficial effect of transcatheter aortic valve implantation (TAVI) on reducing ventricular arrhytmias beyond relieving symptoms in patients with symptomatic severe aortic stenosis.[1] Basically, we showed a reduction in myocardial repolarization dispersion evaluated by QT dispersion (QTd) after TAVI in this population. QTd is the most frequently used non-invasive method to assess the myocardial repolarization abnormalities in many diseases in literature. It has been well known that QTd may provide prognostic data for future ventricular tachyarrhythmias and sudden death.[2]–[4] However, ‘achilles heel’ of this method is the reproducibility of QTd measurements. In general, it is low in both manual and automatic measurement techniques and inter- and intraobserver variability is especially high in manual measurements of QTd.[5],[6] This situation was chiefly caused by using insufficient quality of electrocardiography (ECG) samples to measurement of QTd. Such ECG's do not reflect the end of T wave with sufficient certainty. Therefore, using the appropriate ECG samples is essential to obtain the reliable data on myocardial dispersion abnormalities by QTd. In our study, we used only ECG samples which have high quality. And, we believe that our results are reliable and have future perspectives on the effects of TAVI beyond relieving symptoms in patients with symptomatic severe aortic stenosis. On the other hand, the notion of ‘transmural dispersion’ has emerged in early last decade and has led to a new perception on the understanding of myocardial repolarization. According to this model, it has been accepted that three layer of myocardium including endocardium, epicardium and mid myocardial M cells have different electrophysiological features which represents a repolarization heterogenity in basal situation.[7] Conditions affecting the myocardial repolarization such as heart rate, blood electrolyte status and drugs have a different effects on these myocardial layers which can increase the basal repolarization heterogenity and can cause ventricular arrhytmia. On ECG, the peak of T-wave represents the epicardial repolarization while the end of T-wave suggests the repolarization of midmyocardial M-cells. The time between the peak and end of the T wave is called ‘Tp-e interval’ and its ratio with QTd (Tp-e/QTd) were defined as indexes of transmural dispersion of repolarization which can predict life treating arrhytmias in different populations.[8],[9] We evaluated the Tp-e interval and Tp-e/QTd ratio on ECG of patients in our study group to comply with the author's suggestions. Both Tp-e interval and Tp-e/QTd ratio were significantly reduced after TAVI procedure in patients with severe aortic stenosis (80.1 ± 3.5 vs. 78.5 ± 2.6 ms; P = 0.008 and 0.20 ± 0.1 vs. 0.19 ± 0.1; P = 0.001, respectively). We agree with the authors that the results might be useful to completely reveal of effect of TAVI procedure on electrical heterogeneity of the myocardium.